This invention relates to a portable device having information within a identification card (ID card) etc. and an outside reading device, more particularly to transference of information among those correctly.
As an information card reader for reading an information data from an information card consisting of an ID card, there proposed hitherto is such a one as shown in the U.S. application Ser. No. 294,051 (filed on Jan. 6, 1989). This information card reader is a construction of an information card reading system wherein, as shown in FIG. 1, an answer request signal W1 with, for example, 2.45 [G Hz] microwave as a carrier wave is generated in an answer request signal generation circuit 2 of an information reader 1 and is sent to an information card 4 through a sending antenna 3, an answer information signal W2 sent back from the information card 4 is loaded in an answer signal processing circuit 6 through a receiving antenna 5 of the information reader 1, thereby checking gate-passers bearing the information card 4 as an identification card or freight with the information card 4 stuck thereon as a tag.
Proposed hitherto as the information card 4 applicable to such information card reading system, is that in which a dipole antenna 4B stuck on a substrate 4A so as to form a part of wiring pattern, an information signal generation circuit 4C in a configuration of integrated circuit (IC) for forming an information signal and a power battery 4D are connected by a wiring pattern 4E, an impedance at a feeding point of the dipole antenna 4B is adjusted according to the information signal generated in the information signal generation circuit 4C, and thus a reflection factor to a carrier wave discharged from the information reader 1 as the answer request signal W1 is modified, thereby sending back the reflected wave as the answer information signal W2.
The information generation circuit 4C has an electrical circuit configuration shown in FIG. 2, operating such that an information data S1 loaded in an information memory 11 constructed, for example, of P-ROM with an ID code put before-hand is read by an address signal S3 of an address counter 13 operating according to a clock signal S2 of a clock oscillation circuit 12, and is fed to an impedance variable circuit 14 consisting, for example, of a field effect transistor.
The impedance variable circuit 14 is connected between a pair of feeding point terminals T1 and T2 of the dipole antenna 4B, and thus when the information data S1 becomes a logic "1" or a logic "0" the field effect transistor comes to ON/OFF operation, the impedance at the feeding point of the dipole antenna 4B connected to the feeding point terminals T1 and T2 is subjected to a variable control, thus controlling a reflection factor to the answer request signal W1 incident on the dipole antenna 4B.
The power battery 4D is connected between the feeding point terminal T1 of the information signal generation circuit 4C on a ground side and a power terminal T3, which is ready for controlling an impedance at the feeding point of the dipole antenna 4B continuously at all times according to the information data S1.
An intrinsic ID code is assigned to the information card 4 in the information memory 11, thus the information reader 1 reading an information data incorporated in the information card 4 upon identifying the ID code.
Meanwhile, a signal level of the answer information signal W2 arriving at the receiving antenna 5 from the information card 4 constructed as above is faint substantially, and further a data transmission rate and phase of the answer information signal W2 fluctuate according to an operating state of the information card 4.
By the way, the data transmission rate of the answer information signal W2 is determined on an oscillation frequency in the clock oscillation circuit 12 of the information signal generation circuit 4C, and the oscillation frequency fluctuates inevitably to a great extent (3 times to 10 times for example) according to a change in ambient temperature of the information card 4 in addition to a dispersion caused at the time of IC production or according to a dispersion of power battery at all information cards 4.
Particularly, there is a tendency toward using that simple of a construction and small size as the clock oscillation circuit 12 mountable of the information card 4 so as to cope with a miniaturization of the information card 4, and thus a circuit of CR oscillator construction susceptible to ambient temperature practically is applied thereto, therefore a fluctuation in oscillation frequency is quite unavoidable.
In addition thereto, an external noise of signal level exceedingly high as compared with the signal level of the answer information signal W2 arrives at the receiving antenna 5. The external noise includes, for example, that of the answer request signal W1 sent from the sending antenna 3 which arrives directly at the receiving antenna 5, that of the answer request signal W1 having arrived at the receiving antenna 5 through reflection on wall and others present around the information card 4, that of having arrived from a noise source such as fluorescent lamp or the like, that of the answer request signal W1 sent from other information reader 1 when the information reader 1 is provided more than one, that of being generated as a beat component of the answer request signal W1 from the other information reader 1 and the self answer request signal W1 and others, and the signal level of these noise components becomes so high inevitably as compared with the answer request signal W2 obtainable practically as a reflected wave from the information card 4.
In the information card 4 under such severe noise conditions hitherto, where an information data stored in the information memory 11 is sent, such technique as will send it at a time is employed (Japanese Patent Application Laid Open No. 2-93845, for example).
However, if there arises a phenomenon wherein a carrier wave signal is interrupted practically while the information data is transmitted, then there may be a disadvantage such that an effective information data cannot be present until a first data of the information data is started for transmission again after a transmission of the ensuing information data is kept going to the end.